INDIANAPOLIS -- The American Federation of Teachers says Indiana should immediately suspend its A-F school grading system because of emails showing former schools chief Tony Bennett and his staff changed the grading formula to benefit a top GOP donor's school.

The union issued its call at a Statehouse news conference Thursday, just hours after Bennett resigned as Florida's education commissioner.

Indiana uses A-F grades to determine which schools get taken over by the state and whether students seeking state-funded vouchers to attend private school need to first spend a year in public school. They also help determine how much state funding schools receive.

The grades' validity has been questioned since The Associated Press disclosed emails showing Bennett and his staff worked to raise Christel House Academy from a C to an A.